TSTEPNL (Parameters for Nonlinear Transient Analysis)

Description

The TSTEPNL entry defines a set of parameters for nonlinear transient analysis.

Format

1	2	3	4	5	6	7	8	9	10
TSTEPNL	ID	NDT	DT	NO	NUMRST	KEEP	RTIME

Example

TSTEPNL

120

200

0.001

Field	Definition	Type	Default
SID	Identification number. See Remark 1.	Integer > 0	Required
NDT	Used to specify the duration of the analysis step. The duration is computed as NDT*DT. See Remark 2.	Integer > 0	Required
DT	Time increment between output writes. See Remark 3.	Real > 0.0	Required
NO	Specifies time increment between binary output writes during the analysis. The time increment between binary output writes is NO*DT. See Remark 4.	Integer > 0	0
NUMRST	Number of restart checkpoints to write during the duration of the step specified on the TSTEPNL option that references this RESTARTW option. If this value is zero or negative only one restart checkpoint is written at the end of the duration. See Remarks 5, 6, & 7.	Integer > 0	1
KEEP	Number of restart files to keep. See Remarks 7 & 8.	Integer ≥ -1 or blank	-1
RTIME	Restart read time. Specifies checkpoint time within the restart file specified with the RESTARTR option. See Remark 9.	Real ≥ 0 or blank	blank

Remarks

1. The TSTEPNL Bulk Data entry must be selected by the Case Control command TSTEPNL = ID. Each solution subcase requires a TSTEPNL command and either applied loads via TLOADi data or initial values from a previous subcase. Multiple subcases are assumed to occur sequentially in time with the initial values of time and displacement conditions of each subcase. Initial conditions specified using the IC Case Control command apply only to the first subcase.
2. NDT and DT are used to define the total duration for analysis, which is NDT*DT. Since the explicit time integration method computes the time increment automatically (based upon stability considerations), the actual number of time steps will usually be a much larger number than NDT.
3. DT is not the time increment used in the analysis. It is the time between binary output writes.
4. Results output is generated at times 0.0, 1*DT, 2*DT … NO*DT. A poor choice of DT and NO can result in very large files. Typically you want to choose values so that 20 to 50 results time frames are saved. Note the default value of 1 gives you NDT+1 results times written to the results file.
5. Large values of NUMRST can result in very large files. Typically the value of NUMRST is set to a value on the order of 10 to 20. A results output always occurs at time zero of the step. Therefore you will always get NUMRST+1 output times on the file.
6. If NUMRST is zero or blank, only one restart checkpoint will be written at the end of the step.
7. The NUMRST option can generate extremely large files. Typically this value is set on the order of 10 to 20. If a more frequent number of restart checkpoints is desired, it is highly recommended you use the KEEP option to retain only the last few restarts on the permanent file.
8. If the KEEP option is not used (value negative or zero), all the checkpoints are written into a single file for restart. The restart file name will be constructed from the base file name plus the “.rst.xml” file extension. If the KEEP option is used, the file names will be constructed as base file names plus the time of the restart checkpoint plus the “.rst.xml” file extension. Only KEEP files will be retained on permanent storage and the code will delete restart files as they become obsolete based upon the KEEP parameter.
9. If a restart reading file has been specified using the RESTARTR option, the RTIME value specifies the checkpoint time within the file from which to read. The time specified must be close to one of the times on the file (a tolerance of 0.01 is used to define “close”). If no value is specified here (the field is blank) but a RESTARTR option was used to specify a valid restart file, the last checkpoint time in the file is used for the restart.